1. Field of the Invention
The present invention relates to high-frequency transmission-lines, and more particularly relates to a transmission-line having a line transition device between a dielectric waveguide and a waveguide. Moreover, the invention relates to a primary radiator, an oscillator, and a transmitter which use a line transition device.
2. Description of the Related Art
Dielectric waveguides and waveguides have been used as transmission lines for high frequencies, such as the microwave band, and the millimeter wave band. A typical example of a dielectric waveguide is a non-radiative dielectric (NRD) waveguide. A typical example of a waveguide is a hollow tube through which microwave electromagnetic radiation can be transmitted with relatively slight attenuation. Waveguides often have a rectangular cross section, but some have a circular cross section.
A line transition device between a dielectric waveguide and a waveguide is disclosed, for example, in Japanese Laid-open Patent Application No. 8-70205, which corresponds to U.S. Pat. No. 5,724,013, in which the line transition device between the dielectric waveguide and the waveguide is constructed by tapering an edge of a dielectric strip of the dielectric waveguide and expanding an edge of the waveguide into a horn-shape. The cross-sectional shape of the waveguide used for a line transition is normally rectangular. Line transition devices using a waveguide having a circular cross section are used infrequently.
However, the end face of the dielectric strip, and metal parts of the dielectric waveguide and of the waveguide must be shaped into a special form to realize the above-described tapered or horn-shapes. Thus, the transition becomes large. Moreover, such a line transition device is not suitable for changing the propagating direction of a signal because a bend at the transition causes lowering of the transmission efficiency.
In a multi-layered circuit, a structure which causes a dielectric waveguide in each layer to be electromagnetically coupled is disclosed, for example, in Japanese Laid-open Patent Application No. 8-181502. In the application, a through-hole passing through a layer is provided, and an edge of the dielectric waveguide is disposed in proximity to an end of the through-hole, whereby both dielectric waveguides are electromagnetically coupled through the through-hole.
This structure requires a reflector or the like to shield the through-hole, apart from a connection part between the through-hole and the dielectric waveguide, so that a signal propagating from the dielectric waveguide to the through-hole does not leak, which results in a higher cost.
One example of an antenna device using a dielectric waveguide is disclosed in Japanese Laid-open Patent Application No. 8-316727. A dielectric resonator is disposed in the proximity of an edge of the dielectric strip so as to be electromagnetically coupled with the dielectric strip. A high-frequency signal propagating through the dielectric strip is radiated from the dielectric resonator. The dielectric waveguide and the dielectric resonator are disposed between a pair of conductive plates facing each other. A slit is provided in the upper conductive plate adjacent to the dielectric resonator. An electromagnetic wave is radiated from the slit.
However, because the dielectric resonator is used as a primary radiator, it is difficult to expand a frequency band of the antenna.